[edk2-devel] [PATCH v1 0/8] Measured SEV boot with kernel/initrd/cmdline

[Laszlo Ersek]

On 05/25/21 07:31, Dov Murik wrote:
> Booting with SEV prevented the loading of kernel, initrd, and kernel
> command-line via QEMU fw_cfg interface because they arrive from the VMM
> which is untrusted in SEV.
> 
> However, in some cases the kernel, initrd, and cmdline are not secret
> but should not be modified by the host.  In such a case, we want to
> verify inside the trusted VM that the kernel, initrd, and cmdline are
> indeed the ones expected by the Guest Owner, and only if that is the
> case go on and boot them up (removing the need for grub inside OVMF in
> that mode).
> 
> This patch series declares a new page in MEMFD which will contain the
> hashes of these three blobs (kernel, initrd, cmdline), each under its
> own GUID entry.  This tables of hashes is populated by QEMU before
> launch, and encrypted as part of the initial VM memory; this makes sure
> theses hashes are part of the SEV measurement (which has to be approved
> by the Guest Owner for secret injection, for example).  Note that this
> requires a new QEMU patch which will be submitted soon.
> 
> OVMF parses the table of hashes populated by QEMU (patch 5), and as it
> reads the fw_cfg blobs from QEMU, it will verify each one against the
> expected hash (kernel and initrd verifiers are introduced in patch 6,
> and command-line verifier is introduced in patches 7+8).  This is all
> done inside the trusted VM context.  If all the hashes are correct, boot
> of the kernel is allowed to continue.
> 
> Any attempt by QEMU to modify the kernel, initrd, cmdline (including
> dropping one of them), or to modify the OVMF code that verifies those
> hashes, will cause the initial SEV measurement to change and therefore
> will be detectable by the Guest Owner during launch before secret
> injection.
> 
> Cc: Laszlo Ersek <lersek at redhat.com>
> Cc: Ard Biesheuvel <ardb+tianocore at kernel.org>
> Cc: Jordan Justen <jordan.l.justen at intel.com>
> Cc: Ashish Kalra <ashish.kalra at amd.com>
> Cc: Brijesh Singh <brijesh.singh at amd.com>
> Cc: Erdem Aktas <erdemaktas at google.com>
> Cc: James Bottomley <jejb at linux.ibm.com>
> Cc: Jiewen Yao <jiewen.yao at intel.com>
> Cc: Min Xu <min.m.xu at intel.com>
> Cc: Tom Lendacky <thomas.lendacky at amd.com>
> 
> James Bottomley (8):
>   OvmfPkg/AmdSev/SecretDxe: fix header comment to generic naming
>   OvmfPkg: PlatformBootManagerLibGrub: Allow executing kernel via fw_cfg
>   OvmfPkg/AmdSev: add a page to the MEMFD for firmware config hashes
>   OvmfPkg/QemuKernelLoaderFsDxe: Add ability to verify loaded items
>   OvmfPkg/AmdSev: Add library to find encrypted hashes for the FwCfg
>     device
>   OvmfPkg/AmdSev: Add firmware file plugin to verifier
>   OvmfPkg: GenericQemuLoadImageLib: Allow verifying fw_cfg command line
>   OvmfPkg/AmdSev: add SevQemuLoadImageLib
> 
>  OvmfPkg/OvmfPkg.dec                                                       |  10 ++
>  OvmfPkg/AmdSev/AmdSevX64.dsc                                              |   9 +-
>  OvmfPkg/AmdSev/AmdSevX64.fdf                                              |   3 +
>  OvmfPkg/AmdSev/Library/SevFwCfgVerifier/SevFwCfgVerifier.inf              |  30 +++++
>  OvmfPkg/AmdSev/Library/SevHashFinderLib/SevHashFinderLib.inf              |  34 ++++++
>  OvmfPkg/AmdSev/Library/SevQemuLoadImageLib/SevQemuLoadImageLib.inf        |  30 +++++
>  OvmfPkg/Library/PlatformBootManagerLibGrub/PlatformBootManagerLibGrub.inf |   2 +
>  OvmfPkg/ResetVector/ResetVector.inf                                       |   2 +
>  OvmfPkg/AmdSev/Include/Library/SevHashFinderLib.h                         |  47 ++++++++
>  OvmfPkg/Include/Library/QemuFwCfgLib.h                                    |  35 ++++++
>  OvmfPkg/Library/PlatformBootManagerLibGrub/BdsPlatform.h                  |  11 ++
>  OvmfPkg/AmdSev/Library/SevFwCfgVerifier/SevFwCfgVerifier.c                |  60 ++++++++++
>  OvmfPkg/AmdSev/Library/SevHashFinderLib/SevHashFinderLib.c                | 126 ++++++++++++++++++++
>  OvmfPkg/AmdSev/Library/SevQemuLoadImageLib/SevQemuLoadImageLib.c          |  52 ++++++++
>  OvmfPkg/AmdSev/SecretDxe/SecretDxe.c                                      |   2 +-
>  OvmfPkg/Library/GenericQemuLoadImageLib/GenericQemuLoadImageLib.c         |  29 +++++
>  OvmfPkg/Library/PlatformBootManagerLibGrub/BdsPlatform.c                  |   5 +
>  OvmfPkg/Library/PlatformBootManagerLibGrub/QemuKernel.c                   |  50 ++++++++
>  OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.c                     |  31 +++++
>  OvmfPkg/ResetVector/Ia16/ResetVectorVtf0.asm                              |  20 ++++
>  OvmfPkg/ResetVector/ResetVector.nasmb                                     |   2 +
>  21 files changed, 587 insertions(+), 3 deletions(-)
>  create mode 100644 OvmfPkg/AmdSev/Library/SevFwCfgVerifier/SevFwCfgVerifier.inf
>  create mode 100644 OvmfPkg/AmdSev/Library/SevHashFinderLib/SevHashFinderLib.inf
>  create mode 100644 OvmfPkg/AmdSev/Library/SevQemuLoadImageLib/SevQemuLoadImageLib.inf
>  create mode 100644 OvmfPkg/AmdSev/Include/Library/SevHashFinderLib.h
>  create mode 100644 OvmfPkg/AmdSev/Library/SevFwCfgVerifier/SevFwCfgVerifier.c
>  create mode 100644 OvmfPkg/AmdSev/Library/SevHashFinderLib/SevHashFinderLib.c
>  create mode 100644 OvmfPkg/AmdSev/Library/SevQemuLoadImageLib/SevQemuLoadImageLib.c
>  create mode 100644 OvmfPkg/Library/PlatformBootManagerLibGrub/QemuKernel.c
> 

I'm confirming that this series is in my review queue.

However, I may need unusually long time to get to it. Thanks for your
patience.

Thanks
Laszlo



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